Methods and apparatus for multiple line intra prediction in video compression

ABSTRACT

There is includes a method and apparatus comprising computer code configured to cause a hardware processor or processors to perform intra prediction among a plurality of reference lines, to set a plurality of intra prediction modes for a zero reference line nearest to a current block of the intra prediction among non-zero reference lines, and to set one or more most probable modes for one of the non-zero reference lines.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a Continuation of Nonprovisional applicationU.S. Ser. No. 16/234,324 filed on Dec.27, 2018, which claims priority toProvisional Application U.S. 62/694,132, filed on Jul. 5, 2018. Each ofthe above application(s) is hereby expressly incorporated by reference,in its entirety, into the present application.

BACKGROUND 1. Field

The present disclosure is directed to next-generation video codingtechnologies beyond HEVC, and more specifically, to improvements tointra prediction scheme using multiple reference lines, for example.

2. Description of Related Art

The video coding standard HEVC (High Efficiency Video Coding) mainprofile was finalized in 2013. Soon after that the internationalstandard organizations, ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC29/WG 11), started exploring the needs for developing a future videocoding standard with the potential to significantly enhance thecompression capability compared with the current HEVC standard(including its current extensions). The groups are working together onthis exploration activity in a joint collaboration effort known as theJoint Video Exploration Team (JVET) to evaluate compression technologydesigns proposed by their experts in this area. A Joint ExplorationModel (JEM) has been developed by JVET to explore the video codingtechnologies beyond the capability of HEVC, and current latest versionof JEM is JEM-7.1.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published theH.265/HEVC (High Efficiency Video Coding) standard in 2013 (version 1)2014 (version 2) 2015 (version 3) and 2016 (version 4). Since then theyhave been studying the potential need for standardization of futurevideo coding technology with a compression capability that significantlyexceeds that of the HEVC standard (including its extensions). In October2017, they issued the Joint Call for Proposals on Video Compression withCapability beyond HEVC (CfP). By Feb. 15, 2018, total 22 CfP responseson standard dynamic range (SDR), 12 CfP responses on high dynamic range(HDR), and 12 CfP responses on 360 video categories were submitted,respectively. In April 2018, all received CfP responses were evaluatedin the 122 MPEG/10th JVET (Joint Video Exploration Team-Joint VideoExpert Team) meeting. With careful evaluation, JVET formally launchedthe standardization of next-generation video coding beyond HEVC, i.e.,the so-called Versatile Video Coding (VVC). The current version of VTM(VVC Test Model), i.e., VTM 1.

Even if multiple lines are available, there are various technicalproblems in the art. For example, there is a technical problem in whichit is found that a first reference line is still the most selected line.However, each block with first reference line always needs to signal onebin to indicate the line index of the current block.

Further, multiple line intra prediction is only applied to luma intraprediction. The potential coding gain of multiple line intra predictionwith chroma component is not exploited.

Further, reference samples with different line indexes may havedifferent characteristics by which it is not optimal to set the samenumber of intra prediction modes for different reference lines.

Further, for multiple line intra prediction, the pixels of multipleneighboring lines have been stored and accessed; however, pixels in theneighboring lines are not exploited to smooth the pixels in the currentline.

Further, for multiple line intra prediction, the encoder selects onereference line to predict the pixel values in the current block;however, the variation trend of the neighboring pixels is not exploitedto predict the samples in the current block.

Further, for multiple line intra prediction, there is no planar or DCmode for number>1. The exploration of the other versions of DC or planarmode are not fully exploited.

Further, multiple line reference pixels are applied to intra prediction;however, there are also other places where they use reference pixels,but the coding gain of multiple line reference pixels are not exploited.

Therefore, there is a desire for a technical solution to such problems.

SUMMARY

There is included a method and apparatus comprising memory configured tostore computer program code and a hardware processor or processorsconfigured to access the computer program code and operate as instructedby the computer program code. The computer program includes intraprediction code, configured to cause the processor to code or decode avideo sequence by performing intra prediction among a plurality ofreference lines of the video sequence, intra prediction mode code,configured to cause the processor to set intra prediction modes for afirst reference line, a zero reference line, nearest to a current blockof the intra prediction among a plurality of non-zero reference lines,and most probable mode code configured to cause the processor to set oneor more most probable modes for a second reference line, on of thenon-zero reference lines.

According to exemplary embodiments, the program code further includessignaling code configured to cause the processor to signal a referenceline index before signaling a most probable mode flag and an intra mode,to signal, in response to determining that the reference line index issignaled and that a signaled index indicates the zero reference line,the most probable mode flag, and, in response to determining that thereference line index is signaled and that a signaled index indicates atleast one of the non-zero reference lines, derive the most probable modeflag to be true, without signaling the most probable mode flag, andsignal a most probable mode index of the current block.

According to exemplary embodiments, the most probable mode code isfurther configured to cause the processor to include the one or moremost probable modes in a most probable mode list and to exclude a planarmode and a DC mode from the most probable modes list.

According to exemplary embodiments, the most probable mode code isfurther configured to cause the processor to set a length of the mostprobable mode list based on a reference line index value such that thelength of the most probable mode list comprises a number of the one ormore most probable modes.

According to exemplary embodiments, the most probable mode code isfurther configured to cause the processor to set, in response todetecting the non-zero reference line, the length of the most probablemode list either to 1 or to 4 and to set, in response to determiningthat a current reference line is a zero reference line, the length ofthe most probable mode list to 3 or 6.

According to exemplary embodiments, the most probable mode code isfurther configured to cause the processor to set, in response todetecting the non zero reference line, the length of the most probablemode list to consist of five most probable modes.

According to exemplary embodiments, wherein one of the non-zeroreference lines is a neighboring line to the current block and isfurther away from the current block than the zero reference line.

According to exemplary embodiments, the one or more most probable modescomprise any level of most probable mode from a lowest level mostprobable mode to a highest level most probable mode.

According to exemplary embodiments, the one or more most probable modescomprise only levels of the most probable modes allowed for the non-zeroreference line.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIGS. 1-8 are schematic illustrations of diagrams in accordance withembodiments.

FIGS. 9-14 are simplified flow charts in accordance with embodiments.

FIG. 15 is a schematic illustration of a diagram in accordance withembodiments.

FIGS. 16-25 are simplified flow charts in accordance with embodiments.

FIG. 26 is a schematic illustration of a diagram in accordance withembodiments.

DETAILED DESCRIPTION

The proposed features discussed below may be used separately or combinedin any order. Further, the embodiments may be implemented by processingcircuitry (e.g., one or more processors or one or more integratedcircuits). In one example, the one or more processors execute a programthat is stored in a non-transitory computer-readable medium. In thepresent disclosure, most probable mode (MPM) can refer to a primary MPM,a secondary MPM, or both a primary and a secondary MPM.

FIG. 1 illustrates a simplified block diagram of a communication system100 according to an embodiment of the present disclosure. Thecommunication system 100 may include at least two terminals 102 and 103interconnected via a network 105. For unidirectional transmission ofdata, a first terminal 103 may code video data at a local location fortransmission to the other terminal 102 via the network 105. The secondterminal 102 may receive the coded video data of the other terminal fromthe network 105, decode the coded data and display the recovered videodata. Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals 101 and 104 provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal 101 and 104 may code video data captured at a locallocation for transmission to the other terminal via the network 105.Each terminal 101 and 104 also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals 101, 102, 103 and 104 may be illustrated asservers, personal computers and smart phones but the principles of thepresent disclosure are not so limited. Embodiments of the presentdisclosure find application with laptop computers, tablet computers,media players and/or dedicated video conferencing equipment. The network105 represents any number of networks that convey coded video data amongthe terminals 101, 102, 103 and 104, including for example wirelineand/or wireless communication networks. The communication network 105may exchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network 105may be immaterial to the operation of the present disclosure unlessexplained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem 203, that can includea video source 201, for example a digital camera, creating, for example,an uncompressed video sample stream 213. That sample stream 213,depicted as a bold line to emphasize a high data volume when compared toencoded video bitstreams, can be processed by an encoder 202 coupled tothe camera 201. The encoder 202 can include hardware, software, or acombination thereof to enable or implement aspects of the disclosedsubject matter as described in more detail below. The encoded videobitstream 204, depicted as a thin line to emphasize the lower datavolume when compared to the sample stream, can be stored on a streamingserver 205 for future use. One or more streaming clients 212 and 207 canaccess the streaming server 205 to retrieve copies 208 and 206 of theencoded video bitstream 204. A client 212 can include a video decoder211 which decodes the incoming copy of the encoded video bitstream 208and creates an outgoing video sample stream 210 that can be rendered ona display 209 or other rendering device (not depicted). In somestreaming systems, the video bitstreams 204, 206 and 208 can be encodedaccording to certain video coding/compression standards. Examples ofthose standards are noted above and described further herein.

FIG. 3 may be a functional block diagram of a video decoder 300according to an embodiment of the present invention.

A receiver 302 may receive one or more codec video sequences to bedecoded by the decoder 300; in the same or another embodiment, one codedvideo sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel 301, which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver 302 may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver 302 may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory 303 may be coupled inbetween receiver 302 and entropy decoder/parser 304 (“parser”henceforth). When receiver 302 is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer 303 may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer 303 may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder 300 may include a parser 304 to reconstruct symbols313 from the entropy coded video sequence. Categories of those symbolsinclude information used to manage operation of the decoder 300, andpotentially information to control a rendering device such as a display312 that is not an integral part of the decoder but can be coupled toit. The control information for the rendering device(s) may be in theform of Supplementary Enhancement Information (SEI messages) or VideoUsability Information (VUI) parameter set fragments (not depicted). Theparser 304 may parse/entropy-decode the coded video sequence received.The coding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow principles well known to aperson skilled in the art, including variable length coding, Huffmancoding, arithmetic coding with or without context sensitivity, and soforth. The parser 304 may extract from the coded video sequence, a setof subgroup parameters for at least one of the subgroups of pixels inthe video decoder, based upon at least one parameters corresponding tothe group. Subgroups can include Groups of Pictures (GOPs), pictures,tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units(TUs), Prediction Units (PUs) and so forth. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser 304 may perform entropy decoding/parsing operation on thevideo sequence received from the buffer 303, so to create symbols 313.The parser 304 may receive encoded data, and selectively decodeparticular symbols 313. Further, the parser 304 may determine whetherthe particles symbols 313 are to be provided to a Motion CompensationPrediction unit 306, a scaler/inverse transform unit 305, an IntraPrediction Unit 307 or a loop filter 311.

Reconstruction of the symbols 313 can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser 304. The flow of such subgroup control information between theparser 304 and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 200 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit 305. Thescaler/inverse transform unit 305 receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) 313 from the parser 304. It can output blockscomprising sample values, that can be input into aggregator 310.

In some cases, the output samples of the scaler/inverse transform 305can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit 307. In some cases, the intra picture predictionunit 307 generates a block of the same size and shape of the block underreconstruction, using surrounding already reconstructed informationfetched from the current (partly reconstructed) picture 309. Theaggregator 310, in some cases, adds, on a per sample basis, theprediction information the intra prediction unit 307 has generated tothe output sample information as provided by the scaler/inversetransform unit 305.

In other cases, the output samples of the scaler/inverse transform unit305 can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit 306 canaccess reference picture memory 308 to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols 313 pertaining to the block, these samples can be addedby the aggregator 310 to the output of the scaler/inverse transform unit(in this case called the residual samples or residual signal) so togenerate output sample information. The addresses within the referencepicture memory form where the motion compensation unit fetchesprediction samples can be controlled by motion vectors, available to themotion compensation unit in the form of symbols 313 that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory when sub-sample exact motion vectors are in use, motionvector prediction mechanisms, and so forth.

The output samples of the aggregator 310 can be subject to various loopfiltering techniques in the loop filter unit 311. Video compressiontechnologies can include in-loop filter technologies that are controlledby parameters included in the coded video bitstream and made availableto the loop filter unit 311 as symbols 313 from the parser 304, but canalso be responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit 311 can be a sample stream that canbe output to the render device 312 as well as stored in the referencepicture memory 557 for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser 304), the current reference picture 309can become part of the reference picture buffer 308, and a fresh currentpicture memory can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder 300 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver 302 may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder 300 to properly decode the data and/or to more accuratelyreconstruct the original video data. Additional data can be in the formof, for example, temporal, spatial, or signal-to-noise ratio (SNR)enhancement layers, redundant slices, redundant pictures, forward errorcorrection codes, and so on.

FIG. 4 may be a functional block diagram of a video encoder 400according to an embodiment of the present disclosure.

The encoder 400 may receive video samples from a video source 401 (thatis not part of the encoder) that may capture video image(s) to be codedby the encoder 400.

The video source 401 may provide the source video sequence to be codedby the encoder (303) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source 401 may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source 401 may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder 400 may code and compress thepictures of the source video sequence into a coded video sequence 410 inreal time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController 402. Controller controls other functional units as describedbelow and is functionally coupled to these units. The coupling is notdepicted for clarity. Parameters set by controller can include ratecontrol related parameters (picture skip, quantizer, lambda value ofrate-distortion optimization techniques, . . . ), picture size, group ofpictures (GOP) layout, maximum motion vector search range, and so forth.A person skilled in the art can readily identify other functions ofcontroller 402 as they may pertain to video encoder 400 optimized for acertain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder 402 (“sourcecoder” henceforth) (responsible for creating symbols based on an inputpicture to be coded, and a reference picture(s)), and a (local) decoder406 embedded in the encoder 400 that reconstructs the symbols to createthe sample data that a (remote) decoder also would create (as anycompression between symbols and coded video bitstream is lossless in thevideo compression technologies considered in the disclosed subjectmatter). That reconstructed sample stream is input to the referencepicture memory 405. As the decoding of a symbol stream leads tobit-exact results independent of decoder location (local or remote), thereference picture buffer content is also bit exact between local encoderand remote encoder. In other words, the prediction part of an encoder“sees” as reference picture samples exactly the same sample values as adecoder would “see” when using prediction during decoding. Thisfundamental principle of reference picture synchronicity (and resultingdrift, if synchronicity cannot be maintained, for example because ofchannel errors) is well known to a person skilled in the art.

The operation of the “local” decoder 406 can be the same as of a“remote” decoder 300, which has already been described in detail abovein conjunction with FIG. 3. Briefly referring also to FIG. 4, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder 408 and parser 304 can be lossless, theentropy decoding parts of decoder 300, including channel 301, receiver302, buffer 303, and parser 304 may not be fully implemented in localdecoder 406.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder 403 may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine 407 codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder 406 may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder 403. Operations of the coding engine 407 may advantageouslybe lossy processes. When the coded video data may be decoded at a videodecoder (not shown in FIG. 4), the reconstructed video sequencetypically may be a replica of the source video sequence with someerrors. The local video decoder 406 replicates decoding processes thatmay be performed by the video decoder on reference frames and may causereconstructed reference frames to be stored in the reference picturecache 405. In this manner, the encoder 400 may store copies ofreconstructed reference frames locally that have common content as thereconstructed reference frames that will be obtained by a far-end videodecoder (absent transmission errors).

The predictor 404 ay perform prediction searches for the coding engine407. That is, for a new frame to be coded, the predictor 404 may searchthe reference picture memory 405 for sample data (as candidate referencepixel blocks) or certain metadata such as reference picture motionvectors, block shapes, and so on, that may serve as an appropriateprediction reference for the new pictures. The predictor 404 may operateon a sample block-by-pixel block basis to find appropriate predictionreferences. In some cases, as determined by search results obtained bythe predictor 404, an input picture may have prediction references drawnfrom multiple reference pictures stored in the reference picture memory405.

The controller 402 may manage coding operations of the video coder 403,including, for example, setting of parameters and subgroup parametersused for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder 408. The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter 409 may buffer the coded video sequence(s) as created bythe entropy coder 408 to prepare it for transmission via a communicationchannel 411, which may be a hardware/software link to a storage devicewhich would store the encoded video data. The transmitter 409 may mergecoded video data from the video coder 403 with other data to betransmitted, for example, coded audio data and/or ancillary data streams(sources not shown).

The controller 402 may manage operation of the encoder 400. Duringcoding, the controller 405 may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder 400 may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder 400 may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter 409 may transmit additional data withthe encoded video. The video coder 403 may include such data as part ofthe coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

FIG. 5 illustrates intra prediction modes used in HEVC and JEM. Tocapture the arbitrary edge directions presented in natural video, thenumber of directional intra modes is extended from 33, as used in HEVC,to 65. The additional directional modes in JEM on top of HEVC aredepicted as dotted arrows in FIG. 1 (b), and the planar and DC modesremain the same. These denser directional intra prediction modes applyfor all block sizes and for both luma and chroma intra predictions. Asshown in FIG. 5, the directional intra prediction modes as identified bydotted arrows, which is associated with an odd intra prediction modeindex, are called odd intra prediction modes. The directional intraprediction modes as identified by solid arrows, which are associatedwith an even intra prediction mode index, are called even intraprediction modes. In this document, the directional intra predictionmodes, as indicated by solid or dotted arrows in FIG. 5 are alsoreferred as angular modes.

In JEM, a total of 67 intra prediction modes are used for luma intraprediction. To code an intra mode, an MPM list of size 6 is built basedon the intra modes of the neighboring blocks. If intra mode is not fromthe MPM list, a flag is signaled to indicate whether intra mode belongsto the selected modes. In JEM-3.0, there are 16 selected modes, whichare chosen uniformly as every fourth angular mode. In JVET-D0114 andJVET-G0060, 16 secondary MPMs are derived to replace the uniformlyselected modes.

FIG. 6 illustrates N reference tiers exploited for intra directionalmodes. There is a block unit 611, a segment A 601, a segment B 602, asegment C 603, a segment D 604, a segment E 605, a segment F 606, afirst reference tier 610, a second reference tier 209, a third referencetier 608 and a fourth reference tier 607.

In both HEVC and JEM, as well as some other standards such as H.264/AVC,the reference samples used for predicting the current block arerestricted to a nearest reference line (row or column). In the method ofmultiple reference line intra prediction, the number of candidatereference lines (row or columns) are increased from one (i.e. thenearest) to N for the intra directional modes, where N is an integergreater than or equal to one. FIG. 2 takes 4×4 prediction unit (PU) asan example to show the concept of the multiple line intra directionalprediction method. An intra-directional mode could arbitrarily chooseone of N reference tiers to generate the predictors. In other words, thepredictor p(x,y) is generated from one of the reference samples S1, S2,. . . , and SN. A flag is signaled to indicate which reference tier ischosen for an intra-directional mode. If N is set as 1, the intradirectional prediction method is the same as the traditional method inJEM 2.0. In FIG. 6, the reference lines 610, 609, 608 and 607 arecomposed of six segments 601, 602, 603, 604, 605 and 606 together withthe top-left reference sample. In this document, a reference tier isalso called a reference line. The coordinate of the top-left pixelwithin current block unit is (0,0) and the top left pixel in the 1streference line is (−1,−1).

In JEM, for the luma component, the neighboring samples used for intraprediction sample generations are filtered before the generationprocess. The filtering is controlled by the given intra prediction modeand transform block size. If the intra prediction mode is DC or thetransform block size is equal to 4×4, neighboring samples are notfiltered. If the distance between the given intra prediction mode andvertical mode (or horizontal mode) is larger than predefined threshold,the filtering process is enabled. For neighboring sample filtering, [1,2, 1] filter and bi-linear filters are used.

A position dependent intra prediction combination (PDPC) method is anintra prediction method which invokes a combination of the un-filteredboundary reference samples and HEVC style intra prediction with filteredboundary reference samples. Each prediction sample pred[x][y] located at(x, y) is calculated as follows:

pred[x][y]=(wL*R _(−1,y) +wT*R _(x,−1) +wTL*R_(−1,−1)+(64−wL−wT−wTL)*pred[x][y]+32)>>6  (Eq. 2-1)

where R_(x,−1),R_(−1,y) represent the unfiltered reference sampleslocated at top and left of current sample (x, y), respectively, andR_(−1,−1) represents the unfiltered reference sample located at thetop-left corner of the current block. The weightings are calculated asbelow,

wT=32>>((y<<1)>>shift)  (Equation 2-2)

wL=32>>((x<<1)>>shift)  (Equation 2-3)

wTL=−(wL>>4)−(wT>>4)  (Equation 2-4)

shift=(log 2(width)+log 2(height)+2)>>2  (Equation 2-5).

FIG. 7 illustrates a diagram 700 in which weightings (wL, wT, wTL) for(0, 0) and (1, 0) positions inside one 4×4 block are shown.

FIG. 8 illustrates a Local Illumination Compensation (LIC) diagram 800and is based on a linear model for illumination changes, using a scalingfactor a and an offset b. And it is enabled or disabled adaptively foreach inter-mode coded coding unit (CU).

When LIC applies for a CU, a least square error method is employed toderive the parameters a and b by using the neighboring samples of thecurrent CU and their corresponding reference samples. More specifically,as illustrated in FIG. 8, the subsampled (2:1 subsampling) neighboringsamples of the CU and the corresponding samples (identified by motioninformation of the current CU or sub-CU) in the reference picture areused. The IC parameters are derived and applied for each predictiondirection separately.

When a CU is coded with merge mode, the LIC flag is copied fromneighboring blocks, in a way similar to motion information copy in mergemode; otherwise, an LIC flag is signaled for the CU to indicate whetherLIC applies or not.

FIG. 9 illustrates a flowchart 900 according to exemplary embodiments.

At S901, for multiple line intra prediction, instead of setting a samenumber of reference tiers for all blocks, the number of reference tiersfor each block may be adaptively selected. Here, the index of theclosest reference line is denoted as 1.

At S902, the block sizes of above/left block can be used to determinethe number of reference tiers of current block. For example, if thesizes of above and/or left blocks are larger than M×N, the number ofreference tiers for current block is restricted to L. M and N can be 4,8, 16, 32, 64, 128, 256 and 512. L can be 1˜8.

In one embodiment, when M and/or N is equal to or larger than 64, L isset to 1.

In another embodiment, a ratio of a number of above candidate referencerows to a number of left candidate reference columns is the same as theratio of block width to block height. For example, if the current blocksize is M×N, the number of candidates above reference rows is m and thenumber of candidates left reference columns is n, then M:N=m:n.

Alternatively, at S903, the position of last coefficients of left andabove blocks can be used to determine a number of reference tiers forcurrent block. For example, if a position of last coefficient is withina first M×N region for above and/or left blocks, the number of referencetiers for current block is restricted to L, (e.g. L can be 1˜8), M and Ncan be 1˜1024.

In one embodiment, when there is no coefficients in above and/or leftblocks, the number of reference tiers for current block is restricted to1.

In another embodiment, when the coefficients in the above and/or leftblocks are within 2×2 top-left region, the number of reference tiers forcurrent block is restricted to 1˜2.

Alternatively, at S904, the pixel values of reference samples in aboveand/or left blocks can be used to determine the number of referencetiers of current block. For example, if the difference between referenceline with index L_(i) and the reference line with index L_(j)(L_(i)<L_(j)) is quite small, the reference line L_(j) will be removedfrom the reference line list. L_(i) and L_(j) can be 1˜8. In some cases,reference lines with number>1 are all removed, because the differencebetween all the reference lines are quite small. The method to measurethe difference between two reference lines includes, but not limited to,gradient, SATD, SAD, MSE, SNR and PSNR.

In one embodiment, if the average SAD of L_(i) and L_(j) is less than 2,the reference line L_(j) is removed from the reference line list.

Alternatively, at S905, the prediction mode of above and/or left modeinformation can be used to determine the number of reference tiers for acurrent block.

In one embodiment, if the prediction mode of above and/or left blocks isa skip mode, the number of reference tiers for a current block isrestricted to L. L can be 1˜8.

FIG. 10 illustrates a flowchart 1000 according to exemplary embodiments.

At S1001, the reference line index of Chroma can be derived from Luma,both for separated tree or the same tree. Here, the index of the closestreference line is denoted as 1.

At S1002, for the same tree, if the reference line index for theco-located luma block is ≥3, the reference line index of current Chromablock is set to 2. Otherwise, the reference line index of current Chromablock is set to 1.

At S1003, for the separated tree, if the chroma block just covers oneblock in luma component, the reference line index derivation algorithmis the same as 2.a. If the chroma block covers multiple blocks in lumacomponent, the reference line index derivation algorithm can be one ofthe following:

For the co-located blocks in a luma component, if the reference lineindex of majority of the blocks are less than 3, the reference lineindex for a current chroma block is derived as 1. Otherwise, thereference line index for the current chroma block is derived as 2. Themethod to measure majority can include, but not limited to the regionsize of the blocks and the number of the blocks.

Or, for the co-located blocks in luma component, if the reference lineindex of one block is equal to or larger than 3, the reference lineindex for current chroma block is derived as 2. Otherwise, the referenceline index for current chroma block is derived as 1.

alternatively, for the co-located blocks in a luma component, if thereference line index of majority of the blocks are less than 3, thereference line index for a current chroma block is derived as 1.Otherwise, the reference line index for the current chroma block isderived as 2.

Alternatively, at S1004, it is considered whether to use an adaptiveselection, and if so, the methods in FIG. 9 can also be used to restrictthe number of reference tiers for a current chroma block. After applyingmethods of FIG. 9, the number of reference tiers is set L_(C1). Then,the derivation algorithm in S1002 and S1003, or illustrated as S1005 andS1006 in FIG. 10, is also applied to obtain the line index for a currentblock L_(C2). Then, min (L_(C1), L_(C2)) is the final reference lineindex for a current Chroma block.

FIG. 11 illustrates a flowchart 1100 according to an exemplaryembodiment.

At S1101, it is considered that a different reference line has adifferent number of intra prediction modes. Here, the index of theclosest reference line is denoted as 1.

For example, 1^(st) reference line has 67 modes, 2^(nd) reference linehas 35 modes, 3^(rd) reference line has 17 modes, 4^(th) reference linehas 9 modes

For example, 1^(st) reference line has 67 modes, 2^(nd) reference linehas 33 modes, 3^(rd) reference line has 17 modes, 4^(th) reference linehas 9 modes.

Alternatively, at S1102, reference lines with index>1 share the sameintra mode number, but much less than that of 1^(st) line, such as equalto or less than the half of the intra prediction modes of the 1^(st)reference line.

At S1103, for example, only directional intra prediction modes with evenmode index are allowed for reference line with index larger than 1. Asillustrated in FIG. 5, directional intra prediction modes with odd modeindex are marked with a dotted arrow while directional intra predictionmodes with even mode index are marked with a solid arrow.

At S1104, in another example, only directional intra prediction modeswith an even mode index and DC and Planar modes are allowed for areference line with an index larger than 1.

At S1105, in another example, only most probable modes (MPM) are allowedfor nonzero reference lines, including both the first level MPM and thesecond level MPM.

At S1106, in another example, since a reference line index larger than 1is only enabled for even (or odd mode) intra prediction modes, whencoding the intra prediction modes, if a reference line index larger than1 is signaled, the intra prediction modes, e.g., Planar/DC, and odd (oreven) intra prediction modes are excluded from the MPM derivation andlist, excluded from second level MPM derivation and list, and excludedfrom the remaining non-MPM mode list.

At S1107, the reference line index is signaled after signaling of theintra prediction modes, and whether to signal the reference line indexis dependent on the signaled intra prediction mode.

For example, only directional intra prediction modes with an even modeindex are allowed for a reference line with index larger than 1. If thesignaled intra prediction mode is a directional prediction with an evenmode index, the selected reference line index is signaled. Otherwise,only one default reference line, e.g., the nearest reference line, isallowed for intra prediction and no index is signaled.

In another example, only most probable modes (MPM) are allowed forreference lines with index larger than 1. If the signaled intrapredictions are from MPMs, the selected reference line index needs to besignaled. Otherwise, only one default reference line, e.g., the nearestreference line is allowed for intra prediction and no index is signaled.

In another sub-embodiment, reference lines with an index larger than 1are still enabled for all directional intra prediction modes, or allintra prediction modes, and the intra prediction mode index can be usedas the context for entropy coding the reference line index.

In another embodiment, only most probable modes (MPMs) are allowed forreference lines with index larger than 1. In one approach, all MPMs areallowed for reference lines with indices greater than 1. In anotherapproach, a subset of MPMs are allowed for multiple reference lines withindex greater than 1. When MPMs are categorized in multiple levels, inone approach, only some levels of MPMs are allowed for reference lineswith indices greater than 1. In one example, only the lowest level MPMsare allowed for reference lines with indices greater than 1. In anotherexample, only the highest level MPMs are allowed for reference lineswith indices greater than 1. In another example, only the pre-defined(or signaled/indicated) level MPMs are allowed for reference lines withindices greater than 1.

In another embodiment, only non-MPMs are allowed for reference lineswith indices larger than 1. In one approach, all non-MPMs are allowedfor reference lines with indices greater than 1. In another approach, asubset of non-MPMs are allowed for multiple reference lines with indicesgreater than 1. In one example, only the non-MPM associated with an even(or odd) index in descending (or ascending) order of all non-MPM intramode index are allowed for reference lines with indices greater than 1.

In another embodiment, Planar and DC modes are assigned with apre-defined index of MPM mode list.

In one example, the pre-defined index further depends on codedinformation, including but not limited to, block width and height.

In another sub-embodiment, MPMs with given indices are allowed forreference lines with indices larger than 1. The given MPM indices can besignaled or specified in as a high level syntax element, such as insequence parameter set (SPS), picture parameter set (PPS), slice header,or as a common syntax element or parameter for a region of a picture.Only when intra mode of current block equals to one of the given MPMindices, reference line index is signaled.

For example, the length of MPM list is 6, and the index of MPM list is0, 1, 2, 3, 4, and 5. If intra mode of current block is not equal to themode with MPM index 0 and 5, reference lines with index larger than 1 isallowed.

At S1108, in one embodiment, all intra prediction modes are allowed forthe nearest reference line of current block whereas only the mostprobable modes are allowed (or disallowed) for a reference line withindex larger than 1 (or specific index value, e.g., 1).

At S1109, in one embodiment, a most probable mode only includes thefirst level MPM, such as, 3 MPM in HEVC, 6 MPM in JEM (or VTM).

At S1110, in another embodiment, most probable modes can be any level ofMPM from the lowest level MPMs to the highest level MPMs.

At S1111, in another embodiment, only some levels of MPMs are allowedfor reference lines with indices greater than 1.

At S1112, in another embodiment, most probable modes can be only onelevel of MPM, such as the lowest level MPMs, the highest level MPMs orthe predefined level MPMs.

At S1113, in another embodiment, a reference line index is signaledbefore an MPM flag and an intra mode. When a signaled reference lineindex is 1, an MPM flag is also signaled. When a signaled reference lineindex is larger than 1, a MPM flag of a current block is not signaledand a MPM flag of current block is derived as 1. The MPM index of acurrent block is still signaled for a reference line with index largerthan 1.

At S1114, in one embodiment, the MPM list generation process depends ona reference line index value.

In one example, the MPM list generation process, for a reference linewith an index larger than 1, is different than for a reference line withan index equal to 1. For a reference line with an index larger than 1,planar and DC mode is excluded from the MPM list. The length of the MPMlist is the same for all reference lines.

The default MPMs used in the MPM list generation process are dependenton a reference line index. In one example, the default MPMs, associatedwith a reference line with an index larger than 1, are different thanfor those associated with a reference line with an index equal to 1.

At S1115, in one embodiment, the length of MPM list, i.e., a number ofMPMs, depends on a reference line index value.

In another embodiment, the length of MPM list for a reference line indexvalue at 1 is set differently and for a reference line index valuelarger than 1. For example, a length of an MPM list for a reference linewith an index larger than 1 is 1, or 2 shorter than a length of an MPMlist for a reference line index of 1.

In another embodiment, the length of the MPM list, i.e., number of MPMs,for a reference line index larger than one, is 5. The default MPMs foran MPM list generation process is {Ver, HOR, 2, 66, 34} when 65 angularmodes are applied. The order of the default MPM can be any combinationof these 5 listed modes.

At S1116, for angular intra prediction modes which have derived (notsignaled) a reference line index, e.g., odd directional intra predictionmodes, and/or Planar/DC, multiline reference samples are used togenerate the predictors for a current block.

For angular intra prediction modes which have derived (not signaled) areference line index, the prediction sample value is generated using aweighted sum of multiple predictors, wherein each of the multiplepredictors are the prediction generated using one of the multiplereference lines.

In one example, the weighted sum is using {3, 1} weightings applied onthe predictors generated by the first reference line and the secondreference line, respectively.

In another example, the weightings depend on the block size, the blockwidth, the block height, the sample position within the current block tobe predicted, and/or an intra prediction mode.

In one example, for a given angular prediction mode with an odd index,1^(st) reference line is used to generate one prediction block unitPred₁ and a 2^(nd) reference line is used to generate another predictionblock unit. Then, the final prediction value for each pixel in currentblock unit is the weighted sum of these two generated prediction blockunits. This process can be formulated by the Eq. (4-1), where W_(i) isthe same value for all the pixels in the same block. For differentblocks, W_(i) can be the same regardless of intra prediction modes andblock sizes or can be dependent on the intra prediction modes and blockssizes.

Pred′(x,y)=Σ_(i=1) ² W _(i)Pred_(i)(x,y),  (Eq. 4-1)

Alternatively, at S1117, the number of intra prediction modes for eachreference line is derived by the difference between the referencesamples in that line. The method to measure the difference include, butnot limited to gradient, SATD, SAD, MSE, SNR and PSNR.

If both the above row and left column of the reference samples are quitesimilar, the number of modes can reduced to 4, 9, 17 or 35 modes. The 4modes are: planar, DC, vertical, and horizontal modes.

If only an above row of the reference samples are quite similar, themodes in vertical-like prediction modes are down-sampled. In specialcases, only mode 50 is kept, and modes 35˜mode 49 and mode 51˜mode 66are excluded. In order to make the total intra prediction modes as 9, 17or 35, the intra prediction modes in horizontal-like direction arereduced accordingly.

Else if only left column of the reference samples are quite similar, themodes in horizontal-like direction are down-sampled. In special cases,only mode 18 is kept, and modes 2˜mode 17 and mode 19˜mode 33 areexcluded. In order to make the total intra prediction modes as 9, 17 or35, the intra prediction modes in vertical-like direction is reducedaccordingly.

FIG. 12 illustrates a flowchart 1200 according to exemplary embodiments.

At S1201, there is smoothing of each sample in a current reference linebased on the neighboring samples in a current line and its neighboringreference line(s). Here, the index of the closest reference line isdenoted as 1.

At S1202, for each pixel in a current line, all pixels in a referenceline 1˜L can be used to smooth the pixels in current line. L is the maxallowed reference line number for intra prediction, and L can be 1˜8.

At S1203, for the boundary pixels, they can be filtered or not filtered.If they are filtered, each boundary pixel in the same line uses the samefilter. Boundary pixels in the different lines can use differentfilters. For example, the boundary pixels in a 1^(st) reference line canbe filtered by a [3,2,2,1] filter, the boundary pixels in a 2^(nd)reference line can be filtered by a [2,3,2,1] filter, the boundarypixels in a 3^(rd) reference line can be filtered by a [1,2,3,2] filter,and the boundary pixels in a 4^(th) reference line can be filtered by a[1,2,2,3] filter.

At S1204, for the other pixels, the pixels in each line can use the samefilter, and the pixels in different lines can use different filters.Alternatively, for the other pixels, the pixels in different positioncan use different filters. But these filters are pre-defined, and theencoder does not need to signal the index of the filter.

At S1205, alternatively, the filtering operation for each line can be anintra prediction mode and transform size dependent. The filteringoperation is enabled only when the intra prediction mode and thetransform size satisfies a certain condition. For example, the filteringoperation is disabled when the transform size is equal to 4×4 orsmaller.

At S1206, alternatively, rather than a rectangular shape, the filterused to smooth each pixel may have an irregular filter support shape.The filter support shape may be pre-defined and may depend on anyinformation available to both the encoder and the decoder, including butnot limited to: a reference line index, an intra mode, a block heightand/or a width.

Alternatively, at S1207, for each pixel in a 1^(st) reference line, thepixels in a 1^(st) reference line and a 2^(nd) reference line can beused to smooth that pixel. For each pixel in a 2^(nd) reference line,the pixels in a 1^(st) reference line, a 2^(nd) reference line, and a3^(rd) reference line can be used to smooth that pixel. For each pixelin a 3^(rd) reference line, the pixels in a 2^(nd) reference line, a3^(rd) reference line, and a 4^(th) reference line can be used to smooththat pixel. For each pixel in a 4^(th) reference line, the pixels in a3^(rd) reference line and a 4^(th) reference line can be used to smooththat pixel. In other words, for pixels in a 1^(st) reference line and a4^(th) reference line, the pixels in two lines are used to filter eachpixel, and for pixels in a 2^(nd) reference line and a 3^(rd) referenceline, pixels in three lines are used to filter each pixel.

For example, the filtered pixels in a 2^(nd) reference line and a 3^(rd)reference line can be computed from Eq.4-2˜Eq. 4-5.

$\begin{matrix}{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {x,{y - 1}} \right)} + {p\left( {x,{y + 1}} \right)} + {p\left( {{x + 1},y} \right)} + {4*{p\left( {x,y} \right)}}} \right)3}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}2} \right) \\{\mspace{79mu} {{p^{\prime}\left( {x,y} \right)} = \left( {{p\left( {x,{y + 1}} \right)} - {p\left( {x,{y - 1}} \right)} + {p\left( {x,y} \right)}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}3} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {{x - 1},{y - 1}} \right)} + {p\left( {{x - 1},{y + 1}} \right)} + {p\left( {x,{y - 1}} \right)} + {p\left( {x,{y + 1}} \right)} + {p\left( {{x + 1},{y - 1}} \right)} + {p\left( {{x + 1},y} \right)} + {p\left( {{x + 1},{y + 1}} \right)} + {8*{p\left( {x,y} \right)}}} \right)4}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}4} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{w_{1}*{p\left( {{x - 1},y} \right)}} + {w_{2}*{p\left( {{x - 1},{y - 1}} \right)}} + {w_{3}*{p\left( {{x - 1},{y + 1}} \right)}} + {w_{4}*{p\left( {x,{y - 1}} \right)}} + {w_{5}*{p\left( {x,{y + 1}} \right)}} + {w_{6}*{p\left( {{x + 1},{y - 1}} \right)}} + {w_{7}*{p\left( {{x + 1},y} \right)}} + {w_{8}*{p\left( {{x + 1},{y + 1}} \right)}} + {w_{8}*{p\left( {x,y} \right)}}} \right)/\left( {\sum\limits_{i = 1}^{9}w_{i}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}5} \right)\end{matrix}$

The filtered pixels in a 1^(st) reference line can be computed from Eq.4-6˜Eq. 4-10.

$\begin{matrix}{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {x,{y - 1}} \right)} + {p\left( {{x + 1},y} \right)} + {5*{p\left( {x,y} \right)}}} \right)3}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}6} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {x,{y - 1}} \right)} + {p\left( {{x + 1},y} \right)} + {p\left( {x,y} \right)}} \right)2}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}7} \right) \\{\mspace{79mu} {{p^{\prime}\left( {x,y} \right)} = \left( {{2{p\left( {x,y} \right)}} - {p\left( {x,{y - 1}} \right)}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}8} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {{x - 1},{y - 1}} \right)} + {p\left( {x,{y - 1}} \right)} + {p\left( {{x + 1},{y - 1}} \right)} + {p\left( {{x + 1},y} \right)} + {3*{p\left( {x,y} \right)}}} \right)3}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}9} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{w_{1}*{p\left( {{x - 1},y} \right)}} + {w_{2}*{p\left( {{x - 1},{y - 1}} \right)}} + {w_{3}*{p\left( {x,{y - 1}} \right)}} + {w_{4}*{p\left( {{x + 1},{y - 1}} \right)}} + {w_{5}*{p\left( {{x + 1},y} \right)}} + {w_{6}*{p\left( {x,y} \right)}}} \right)/\left( {\sum\limits_{i = 1}^{6}w_{i}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}10} \right)\end{matrix}$

The filtered pixels in a 4^(th) reference line can be computed from Eq.4-11˜Eq. 4-15.

$\begin{matrix}{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {x,{y + 1}} \right)} + {p\left( {{x + 1},y} \right)} + {5*{p\left( {x,y} \right)}}} \right)3}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}11} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {x,{y + 1}} \right)} + {p\left( {{x + 1},y} \right)} + {p\left( {x,y} \right)}} \right)2}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}12} \right) \\{\mspace{79mu} {{p^{\prime}\left( {x,y} \right)} = \left( {{2{p\left( {x,y} \right)}} - {p\left( {x,{y + 1}} \right)}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}13} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{p\left( {{x - 1},y} \right)} + {p\left( {{x - 1},{y + 1}} \right)} + {p\left( {x,{y + 1}} \right)} + {p\left( {{x + 1},{y + 1}} \right)} + {p\left( {{x + 1},y} \right)} + {3*{p\left( {x,y} \right)}}} \right)3}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}14} \right) \\{{p^{\prime}\left( {x,y} \right)} = {\left( {{w_{1}*{p\left( {{x - 1},y} \right)}} + {w_{2}*{p\left( {{x - 1},{y + 1}} \right)}} + {w_{3}*{p\left( {x,{y + 1}} \right)}} + {w_{4}*{p\left( {{x + 1},{y + 1}} \right)}} + {w_{5}*{p\left( {{x + 1},y} \right)}} + {w_{6}*{p\left( {x,y} \right)}}} \right)/\left( {\sum\limits_{i = 1}^{6}w_{i}} \right)}} & \left( {{{Eq}.\mspace{14mu} 4}\text{-}15} \right)\end{matrix}$

In addition, rounding, such as rounding to zero, to positive infinity orto negative infinity, may be added to the above calculations.

FIG. 13 illustrates a flowchart 1300 according to exemplary embodiments.

At S1301, in current block, samples in different position may usedifferent combinations of reference samples with a different line indexprediction. Here, the index of the closest reference line is denoted as1.

At S1302, for a given intra prediction mode, each reference line i cangenerate one prediction block Pred_(i). For the pixels in each position,that mode can use different combination of these generated predictionblock Pred_(i) to generate the final prediction block. To be specific,for the pixel at position (x,y), Eq. 4-16 can be used to calculate theprediction value

Pred′(x,y)=Σ_(i=0) ^(N) W _(i)Pred_(i)(x,y),  (Eq. 4-16)

where W_(i) is position dependent. In other words, the weighting factorsare the same for the same position, and the weighting factors aredifferent for the different positions.

Alternatively, given an intra prediction mode, for each sample, a set ofreference samples from multiple reference lines are selected, and aweighted sum of these selected set of reference samples is calculated asthe final prediction value. The selection of reference samples maydepend on intra mode and position of prediction sample, and theweightings may depend on intra mode and position of prediction sample.

At S1303, when applying reference line x for intra prediction, for eachsample, the prediction value of line 0 and line x is compared, and ifline 1 generates a very different prediction value, then the predictionvalue from line x is excluded, and line 0 may be used instead. The wayto measure the difference between prediction value of current positionand that of its neighboring positions includes, but is not limited to,gradient, SATD, SAD, MSE, SNR and PSNR.

Alternatively, more than two prediction values are generated fromdifferent reference lines, and the median (or average, or mostfrequently appeared) value is used as the prediction sample.

At S1304, when applying reference line x for intra prediction, for eachsample, the prediction value of line 1 and line x is compared, and ifline 1 generates a very different prediction value, then the predictionvalue from line x is excluded, and line 1 may be used instead. The wayto measure the difference between prediction value of current positionand that of its neighboring positions includes, but is not limited togradient, SATD, SAD, MSE, SNR and PSNR.

Alternatively, more than two prediction values are generated fromdifferent reference lines, and the median (or average, or mostfrequently appeared) value is used as the prediction sample.

FIG. 14 illustrates a flowchart 1400 according to exemplary embodiments.

At S1401, after intra prediction, instead of only using the pixels inthe nearest reference line, the pixels in multiple lines are used tofilter the prediction value of each block. Here, the index of theclosest reference line is denoted as 1.

For example, at S1402, PDPC may be extended for multiple line intraprediction. Each prediction sample pred[x][y] located at (x, y) iscalculated as follows:

pred[x][y]=(Σ_(i=m) ⁻¹ wL _(i) *R _(i,y)+Σ_(i=m) ⁻¹ wT _(i) *R_(x,i)+Σ_(i=m) ⁻¹ wTL _(i) *TL _(i,i)+(64−Σ_(i=m) ⁻¹ wL _(i)−Σ_(i=m) ⁻¹wT _(i)−Σ_(i=m) ⁻¹ wTL _(i))*pred[x][y]+32)>>6  (Eq. 4-17)

where m can be −8˜−2.

In one example, reference samples in the nearest two lines are used tofilter the samples in current block. For top-left pixel, only thetop-left sample in the first row are used. It can be formulated by Eq.4-18.

pred[x][y]=(Σ_(i=−2) ⁻¹ wL _(i) *R _(i,y)+Σ_(i=−2) ⁻¹ wT _(i) *R _(x,i)+wTL ⁻¹ * TL _(−1,−1)+(64−Σ_(i=−2) ⁻¹ wL _(i)−Σ_(i=−2) ⁻ wT −wTL⁻¹)*pred[x][y]+32)>>6  (Eq. 4-18)

Alternatively, at S1403, boundary filters can be extended to multiplelines.

After DC prediction, for the pixels in the first several columns and thefirst several rows are filtered by the neighboring reference pixels. Thepixels in the first column can be filtered by

p′(x,y)=(Σ_(i=m) ⁻¹ wL _(i) *R _(i,y)+(64−Σ_(i=m) ⁻¹ wL_(i))*p(x,y))>>6  (Eq. 4-19)

For the pixels in the first row, the filtering operation is as follows

p′(x,y)=(Σ_(i=m) ⁻¹ wT _(i) *R _(x,i)+(64−Σ_(i=m) ⁻¹ wT_(i))*p(x,y))>>6  (Eq. 4-20)

In some special case, pixels in the first column can be filtered by

p′(0,y)=p(0,y)+R _(−1,y) −R _(−2,y)  (Eq. 4-21)

Pixels in the first row can also be filtered by

p′(x,0)=p(x,0)+R _(x,−1) −R _(x,−2)  (Eq. 4-22)

After a vertical prediction, the pixels in the first several columns canbe filtered by Eq. 4-23

p′(x,y)=Σ_(i=m) ⁻¹ wL _(i)*(R _(i,y) −R _(i,i))+p(x,y)  (Eq. 4-23)

After a horizontal prediction, the pixels in the first several rows canbe filtered by Eq. 4-24

p′(x,y)=Σ_(i=m) ⁻¹ wT _(i)*(R _(x,i) −R _(i,i))+p(x,y)  (Eq. 4-24)

In another embodiment, for vertical/horizontal prediction, if thereference line with an index larger than 1 is used to generate theprediction sample, the 1^(st) column/row and its corresponding pixel inthe line index larger than 1 is used for boundary filtering. Asillustrated in FIG. 15, with its reference lines 1503, 1502 and blockunit 1501, 2^(nd) reference line 1503 is used to generate the predictionsample for a current block unit and the pixels with vertical directionare used for vertical prediction. After the vertical prediction, thepixels with a diagonal texture in reference line 1 and the pixel withdiagonal texture in reference line 1503 are used to filter the firstseveral columns in current block unit. The filtering process can beformulated by Eq. 4-25, where m denotes the selected line index, and itcan be 2˜8. n is the number of right shift bits, it can be 1˜8.

p′(x,y)=p(x,y)+(p(−1,y)−p(−1,−m))>>n  (Eq. 4-25)

For horizontal prediction, the filtering process can be formulated byEq. 4-26.

p′(x,y)=p(x,y)+(p(x,−1)−p(−m,−1))>>n  (Eq. 4-26)

In another embodiment, when reference line with index larger than 1 isused, after diagonal predictions, such as mode 2 and mode 34 in FIG. 1(a), pixels along the diagonal direction from the 1^(st) reference lineto current reference line are used for filtering the pixels in the firstseveral columns/rows of current block unit. To be specific, after mode 2prediction, the pixels in the first several rows can be filtered by Eq.4-27. After mode 34 prediction, the pixels in the first several columnscan be filtered by Eq. 4-28. m denotes the reference line index forcurrent block, and it can be 2˜8. n is the number of right shift bits,it can be 2˜8. W_(i) is the weighting coefficients, and it is theinteger.

p′ ^((x,y))=(Σ_(i=1) ^(m) W _(i) R(x+i,−i)+(2^(n)−Σ_(i=1) ^(m) W_(i))*p(x,y)+2^(n−1))>>n   (Eq. 4-27)

p′ ^((x,y))=(Σ_(i=1) ^(m) W _(i) R(−i,y+i)+(2^(n)−Σ_(i−1) ^(m) W_(i))*p(x,y)+2^(n−1))>>n   (Eq. 4-28)

FIG. 16 illustrates a flowchart 1600 according to exemplary embodiments.

At S1601, for multiple reference line intra prediction, modified DC andplanar modes are added when a reference line index is greater than 1.Here, the index of the closest reference line is denoted as 1.

At S1602, for Planar mode, when a different reference line is used,different pre-defined top-right and bottom-left reference samples areused to generate the prediction samples.

At S1603, alternatively, when a different reference line is used,different intra smoothing filter is used.

At S1604, for DC mode, for 1^(st) reference line, all the pixels in theabove row and the left column are used to calculate the DC value, whenreference line index is greater 1, only some of the pixels are used tocalculate the DC value.

For example, above pixels in a 1^(st) reference line are used tocalculate the DC values for a 2^(nd) reference line, left pixels in a1^(st) reference line are used to calculate the DC values for a 3^(rd)reference line, half of left pixels and half of the above pixels in a1^(st) reference line are used to calculate the DC values for the 4^(th)reference line.

At S1605, for DC mode, all reference pixels in all available candidatelines (rows and columns) are used to calculate the DC predictor.

FIG. 17 illustrates a flowchart 1700 according to exemplary embodiments.

At S1701, it is implemented to extend multiple reference lines to ICmode. At S1702, multiple above/left reference lines are used tocalculate IC parameters, and at S1703, which reference line is used tocalculate IC parameters is signaled.

FIG. 18 illustrates a flowchart 1800 according to exemplary embodiments.

At S1801, it is implemented to signal multiple reference line index.

In one embodiment, at S1802, the reference line index is signaled usingvariable length coding. The closer to the current block in distance, theshorter the codeword. For example, if the reference line index is 0, 1,2, 3, with 0 being closest to the current block and 3 the furthest, thecodewords for them are 1, 01, 001, 000, where 0 and 1 can be alternated.

In another embodiment, at S1806, the reference line index is signaledusing fixed length coding. For example, if the reference line index is0, 1, 2, 3, with 0 being closest to the current block and 3 thefurthest, the codewords for them are 10, 01, 11, 00, where 0 and 1 canbe alternated and the order may be altered.

At S1803, it is considered whether to variously use a codeword table andif not, at S1804, in yet another embodiment, the reference line index issignaled using variable length coding, where the order of the indices inthe codeword table (from the shortest codeword to the longest) is asfollows: 0, 2, 4, . . . 2k, 1, 3, 5, . . . 2k+1 (or 2k−1). Index 0indicates the reference line which is the closest to the current blockand 2k+1, the furthest.

In yet another embodiment, at S1805, the reference line index issignaled using variable length coding, where the order of the indices inthe codeword table (from the shortest codeword to the longest) is asfollows: the closest, the furthest, 2^(nd) closest, 2^(nd) furthest, . .. and so on. In one specific example, if the reference line index is 0,1, 2, 3, with 0 being the closest to the current block and 3 thefurthest, the codewords for them are 0 for index 0, 10 for index 3, 110for index 2, 111 for index 1. The codewords for reference line index 1and 2 may be switched. The 0 and 1 in codewords may be altered.

FIG. 19 illustrates a flowchart 1900 according to exemplary embodiments.

At S1901, there is signaling multiple reference line index when thenumber of above reference lines (rows) is different to the number ofleft reference lines (columns).

At S1902, in one embodiment, if the number of above reference lines(rows) is M and the number of left reference lines (columns) is N, thenthe reference line indices for max(M, N) may use any of the methodsdescribed above, or their combinations. The reference line indices formin(M, N) take a subset of the codewords from the codewords used forindicating reference line indices for max(M, N), usually the shorterones. For example, if M=4, N=2, and the codewords used to signal M (4)reference line indices {0, 1, 2, 3} are 1, 01, 001, 000, then thecodewords used to signal N (2) reference line indices {0, 1} are 1, 01.

In another embodiment, at S1903, if the number of above reference lines(rows) is M and the number of left reference lines (columns) is N, andif M and N are different, then the reference line indices for signalingabove reference line (row) index and left reference line (column) indexmay be separate and independently use any method described above ortheir combinations.

FIG. 20 illustrates a flowchart 2000 according to exemplary embodiments.

At S2000, it is considered to find number of reference lines in variouscoding tools, and at S2001, the maximum number of reference lines thatmay be used for intra prediction may be constrained to be no more thanthe number of reference lines used in other coding tools, such as adeblocking filter or a template matching based intra prediction, inorder to potentially save the pixel line buffer.

FIG. 21 illustrates a flowchart 2100 according to exemplary embodiments.

At S2100, interactions between multiple line intra prediction and othercoding tools/modes are implemented.

For example, at S2101, in one embodiment, the usage and/or signaling ofother syntax elements/coding tools/modes, including but not limited to:cbf, last position, transform skip, transform type, secondary transformindex, primary transform index, PDPC index, may depend on the multi-linereference line index.

At S2102, in one example, when a multi-line reference index is nonzero,a transform skip is not used, and a transform skip flag is not signaled.

At S2103, in another example, the context used for signaling othercoding tools, e.g., transform skip, cbf, primary transform index,secondary transform index, may depend on the value of multi-linereference index.

At S2104, in another embodiment, the multi-line reference index may besignaled after other syntax elements, including but not limited to: cbf,last position, transform skip, transform type, secondary transformindex, primary transform index, PDPC index, and the usage and/orsignaling of multi-line reference index may depend on other syntaxelements.

FIG. 22 illustrates a flowchart 2200 according to exemplary embodiments.

At S2201, it is considered to acquire a reference line index, and atS2202, the reference line index can be used as the context for entropycoding another syntax element, including, but not limited to intraprediction mode, MPM index, primary transform index, secondary transformindex, transform skip flag, coding block flag (CBF) and transformcoefficients, or vice versa.

FIG. 23 illustrates a flowchart 2300 according to exemplary embodiments.

It is proposed that, at S2301, to include reference line informationinto the MPM list. That is to say, if the prediction mode of currentblock is the same as one candidate in MPM list, both of the intraprediction and the selected reference line of the selected candidate areapplied for a current block, and the intra prediction mode and referenceline index are not signaled. In addition, the number of the MPMcandidates for different reference line indexes are predefined. Here,the closest reference line is denoted as 1.

At S2302, in one embodiment, the number of MPMs for each reference lineindex is predefined and it can be signaled as a higher level syntaxelement, such as in sequence parameter set (SPS), picture parameter set(PPS), slice header, Tile header, coding tree unit (CTU) header, or as acommon syntax element or parameter for a region of a picture. As aresult, the length of MPM list can be different in different sequences,pictures, slices, Tiles, group of coding blocks or a region of apicture.

For example, the number of MPMs for a reference line index 1 is 6, andthe number of MPMs with each of other reference line indices is 2. As aresult, if the total reference line number is 4, the total number of MPMlist is 12.

In another embodiment, at S2303, all intra prediction modes togetherwith their reference line index in the above, left, top-left, to-right,and bottom-left block are included into the MPM list. As with theillustration 2400 in FIG. 24, showing all neighboring blocks of acurrent block unit and where A is bottom-left block, B, C, D, and E areleft blocks, F is top-left block, G and H are top blocks, and I istop-right block. After adding modes of the neighboring blocks into MPMlist. If the number of MPM candidate with given reference line number isless than the predefined number, default modes are used to fill the MPMlist.

In another embodiment, at S2304, if the mode of current block is equalto one of the candidate in MPM list, the reference line index is notsignaled. If the mode of current block is not equal to any candidate inMPM list, reference line index is signaled.

In one example, if line 1 is used for current block, second level MPMmodes are still used, but a second level MPM only includes the intraprediction mode information.

In another example, for other lines, a second level MPM is not used, anda fixed length coding is used to code the remaining mode.

FIG. 25 illustrates a flowchart 2500 according to exemplary embodiments.

At S2501, in current VVC test mode VTM-1.0, chroma intra coding modesare the same as those in HEVC, including DM (direct copy of luma mode)and 4 additional angular intra prediction modes, in current BMS-1.0, thecross component linear model (CCLM) mode is also applied for chromaintra coding. The CCLM modes include one LM mode, one multi-model LM(MMLM) and 4 multi-filter LM (MFLM) modes, and it is in that light thatonly DM modes are used for chroma blocks when CCLM modes are not enabledwhereas only DM and CCLM modes are used for chroma blocks when CCLMmodes are enabled.

At S2502, in one embodiment, only one DM mode is used for chroma blocksand no flag is signaled for chroma blocks, the chroma mode is derived asDM mode.

In another embodiment, at S2503, only a one DM and one CCLM mode is usedfor chroma blocks and one DM flag is used to signal whether a DM or a LMmode is used for current chroma blocks.

In one sub-embodiment, there are 3 contexts used for signaling the DMflag. When both left and above blocks use DM modes, a context 0 is usedto signal the DM flag. When only one of the left and above blocks usesDM modes, a context 1 is used to signal the DM flag. Otherwise, whenboth left and above blocks do not use DM modes, contexts 2 are used tosignal a DM flag.

In another embodiment, at S2504 only DM and CCLM (when enabled) modesare used for small chroma blocks. When width, or height, or area size(width*height) of the chroma block is less than or equal to Th, currentchroma block is called small chroma block. Th can be 2, 4, 8, 16, 32,64, 128, 256, 512, or 1024.

For example, when the area size of a current chroma block is less thanor equal to 8, only DM and CCLM (when enabled) modes are used forcurrent chroma block.

In another example, when the area size of current chroma block is lessthan or equal to 16, only DM and CCLM (when enabled) modes are used forcurrent chroma block.

In another example, only one DM and one CCLM (when enabled) modes areused for small chroma block.

In another embodiment, at S2505, when the intra mode of luma componentis equal to one of the MPM mode, chroma blocks can only use DM mode andno flag is signaled for chroma mode, otherwise both DM and CCLM modesare allowed for chroma blocks.

In one example, a MPM mode can only be a first level MPM.

In another example, a MPM mode can only be the second level MPM.

In another example, a MPM mode can be either a first level MPM or asecond level MPM.

In another embodiment, at S2506, when an intra mode of a luma componentis not equal to any of the MPM mode, chroma blocks can use a DM mode andno flag is signaled for a chroma mode, otherwise both DM and CCLM modesare allowed for chroma blocks.

Accordingly, by exemplary embodiments described herein, the technicalproblems noted above may be advantageously improved upon by thesetechnical solutions.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media or by a specifically configured one or morehardware processors. For example, FIG. 26 shows a computer system 2600suitable for implementing certain embodiments of the disclosed subjectmatter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 26 for computer system 2600 are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 2600.

Computer system 2600 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 2602, mouse 2603, trackpad 403, touch screen2604, joystick 2605, microphone 2606, scanner 2608, camera 2607.

Computer system 2600 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 2610, or joystick 2605, but there can also be tactilefeedback devices that do not serve as input devices), audio outputdevices (such as: speakers 2609, headphones (not depicted)), visualoutput devices (such as screens 2610 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability—someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 2600 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW2612 with CD/DVD or the like media 2611, thumb-drive 2613, removablehard drive or solid state drive 2614, legacy magnetic media such as tapeand floppy disc (not depicted), specialized ROM/ASIC/PLD based devicessuch as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 2600 can also include interface to one or morecommunication networks 2615. Networks can for example be wireless,wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general-purpose data ports or peripheral buses 2625 (such as,for example USB ports of the computer system 2600; others are commonlyintegrated into the core of the computer system 2600 by attachment to asystem bus as described below (for example Ethernet interface into a PCcomputer system or cellular network interface into a smartphone computersystem). Using any of these networks, computer system 2600 cancommunicate with other entities. Such communication can beuni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbusto certain CANbus devices),or bi-directional, for example to other computer systems using local orwide area digital networks. Certain protocols and protocol stacks can beused on each of those networks and network interfaces as describedabove.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 2612 of thecomputer system 2600.

The core 2612 can include one or more Central Processing Units (CPU)2612, Graphics Processing Units (GPU) 2622, specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)2624, hardware accelerators for certain tasks 2624, and so forth. Thesedevices, along with Read-only memory (ROM) 2619, Random-access memory2618, internal mass storage such as internal non-user accessible harddrives, SSDs, and the like 447, may be connected through a system bus2626. In some computer systems, the system bus 226 can be accessible inthe form of one or more physical plugs to enable extensions byadditional CPUs, GPU, and the like. The peripheral devices can beattached either directly to the core's system bus 2626, or through aperipheral bus 2601. Architectures for a peripheral bus include PCI,USB, and the like.

CPUs 2621, GPUs 2622, FPGAs 2624, and accelerators 2624 can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM2619 or RAM 2618. Transitional data can also be stored in RAM 2618,whereas permanent data can be stored for example, in the internal massstorage 2620. Fast storage and retrieve to any of the memory devices canbe enabled through the use of cache memory, that can be closelyassociated with one or more CPU 2621, GPU 2622, mass storage 2620, ROM2619, RAM 618, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 2600, and specifically the core 2616 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 2616 that are of non-transitorynature, such as core-internal mass storage 2620 or ROM 2619. Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core 2616. A computer-readablemedium can include one or more memory devices or chips, according toparticular needs. The software can cause the core 2616 and specificallythe processors therein (including CPU, GPU, FPGA, and the like) toexecute particular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 2618and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 2624), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

1. A method for video decoding comprising: performing decoding of avideo sequence by intra prediction among a plurality of reference linesof the video sequence; setting a plurality of intra prediction modes fora zero reference line nearest to a current block of the intra predictionamong a plurality of non-zero reference lines; and setting one or moremost probable modes for one of the non-zero reference lines, wherein theone or more probable modes are included in a most probable mode list,and wherein a planar mode and a DC mode are absent from the mostprobably list.
 2. The method according to claim 1, further comprising:signaling a reference line index before signaling a most probable modeflag and an intra mode; signaling the most probable mode flag, inresponse to determining that the reference line index is signaled andthat a signaled index indicates the zero reference line; and in responseto determining that the reference line index is signaled and that asignaled index indicates at least one of the non-zero reference lines,deriving the most probable mode flag to be true, without signaling themost probable mode flag, and signaling a most probable mode index of thecurrent block.
 3. (canceled)
 4. The method according to claim 1, furthercomprising: setting a length of the most probable mode list based on areference line index value such that the length of the most probablemode list comprises a number of the one or more most probable modes 5.The method according to claim 4, further comprising: setting, inresponse to detecting the non-zero reference line, the length of themost probable mode list either to 1 or to 4; and setting, in response todetermining that a current reference line is a zero reference line, thelength of the most probable mode list to 3 or
 6. 6. The method accordingto claim 4, further comprising: setting, in response to detecting thenon-zero reference line, the length of the most probable mode list toconsist of five most probable modes.
 7. The method according to claim 1,wherein the one of the non-zero reference lines is a neighboring line tothe current block and is further away from the current block than thezero reference line.
 8. The method according to claim 1, wherein the oneor more most probable modes consist of a first level most probable mode.9. The method according to claim 1, wherein the one or more mostprobable modes comprise any level of most probable mode from a lowestlevel most probable mode to a highest level most probable mode.
 10. Themethod according to claim 1, wherein the one or more most probable modescomprise only levels of the most probable modes allowed for the non-zeroreference line.
 11. An apparatus comprising: at least one memoryconfigured to store computer program code; at least one hardwareprocessor configured to access the computer program code and operate asinstructed by the computer program code, the computer program codeincluding: decoding code configured to cause the processor to decode avideo sequence by performing intra prediction among a plurality ofreference lines of the video sequence; intra prediction mode codeconfigured to cause the at least one processor to set a plurality ofintra prediction modes for a zero reference line nearest to a currentblock of the intra prediction among a plurality of non-zero referencelines; and most probable mode code configured to cause the at least oneprocessor to set one or more most probable modes for one of the non-zeroreference lines, wherein the most probable mode code is furtherconfigured to cause the at least one processor to include the one ormore most probable modes in a most probable mode list, and wherein aplanar mode and a DC mode are absent from the most probable mode list.12. The apparatus according to claim 11, wherein the program codefurther includes signaling code configured to cause the at least oneprocessor to: signal a reference line index before signaling a mostprobable mode flag and an intra mode; the most probable mode flag issignaled in response to determining that the reference line index issignaled and that a signaled index indicates the zero reference line;and in response to determining that the reference line index is signaledand that a signaled index indicates at least one of the non-zeroreference lines, derive the most probable mode flag to be true, withoutsignaling the most probable mode flag, and signal a most probable modeindex of the current block.
 13. (canceled)
 14. The apparatus accordingto claim 11, wherein the most probable mode code is further configuredto cause the at least one processor to: set a length of the mostprobable mode list based on a reference line index value such that thelength of the most probable mode list comprises a number of the one ormore most probable modes.
 15. The apparatus according to claim 14,wherein the most probable mode code is further configured to cause theat least one processor to: set, in response to detecting the non-zeroreference line, the length of the most probable mode list either to 1 orto 4; and set, in response to determining that a current reference lineis a zero reference line, the length of the most probable mode list to 3or
 6. 16. The apparatus according to claim 15, wherein the most probablemode code is further configured to cause the at least one processor to:set, in response to detecting the non-zero reference line, the length ofthe most probable mode list to consist of five most probable modes. 17.The apparatus according to claim 11, wherein the one of the non-zeroreference lines is a neighboring line to the current block and isfurther away from the current block than the zero reference line. 18.The apparatus according to claim 11, wherein the one or more mostprobable modes consist of a first level most probable mode.
 19. Theapparatus according to claim 11, wherein the one or more most probablemodes comprise any level of most probable mode from a lowest level mostprobable mode to a highest level most probable mode.
 20. Anon-transitory computer readable medium storing a program causing acomputer to execute a process, the process comprising: performingdecoding of a video sequence by intra prediction among a plurality ofreference lines of the video sequence; setting a plurality of intraprediction modes for a zero reference line nearest to a current block ofthe intra prediction among a plurality of non-zero reference lines; andsetting one or more most probable modes for one of the non-zeroreference lines, wherein the one or more most probable modes areincluded in a most probable mode list, and wherein a planar mode and aDC mode are absent from the most probable mode list.